Novel targeted therapeutic for advanced metastatic disease Abstract Despite improved, targeted therapies, lung cancer remains the leading cause of cancer-related mortality worldwide. The five-year survival rate for advanced-stage lung cancer is less than 10%, largely due to metastasis to the CNS. Around 50% of patients diagnosed with either small cell lung cancer (SCLC) or non- small cell lung cancer (NSCLC) will develop metastatic brain lesions. Therapeutics that specifically target the metastatic process are needed. The role of K+ channels in tumorigenesis has been recognized for over a decade. In particular, the two pore-domain channel, KCNK9, exerts a tumorigenic and pro-metastatic effect in several models. Furthermore, KCNK9 is over-expressed from 5- to >100-fold in 44% of breast and 30% of lung tumors. In xenograft models, tumor cells over-expressing KCNK9 are typically aggressive. In the xenograft model, a dominant negative mutant of KCNK9 abolishes its K+ channel activity and abrogates its oncogenic function, without any effect on normal cell growth. These data support the hypothesis that KCNK9 promotes tumor growth and may be a therapeutic target in KCNK9-expressing malignancies. Despite these data suggesting the potential for therapeutics directed against KCNK9, a lack of specific reagents has hindered both research and preclinical studies. We have identified a monoclonal antibody to the extracellular loop domain of KCNK9 and have demonstrated its high specificity and high affinity for the KCNK9 channel. This mAb inhibits the proliferation and viability of KCNK9+ cancer cell lines in vitro. Most importantly for the present work, monoclonal antibodies to KCNK9 potently inhibited the initiation, growth, and metastatic spread of tumors in human xenograft and syngeneic mouse models. These observations instruct the overall goal of this project to develop a monoclonal antibody therapy targeting tumors expressing KCNK9. In Phase I, we will generate a humanized and Fc-enhanced form of murine anti-KCNK9 mAb Y4. We will evaluate binding, specificity, in vitro functional activity, and in vivo anti-tumor activity of huY4. This innovative therapeutic humAb will be the safest and most effective treatment for KCNK9+ tumors with particular application to advanced- stage lung cancer and breast cancer. Demonstration of a humAb with a nanomolar Kd, high specificity for KCNK9, and in vivo anti-tumor activity, will merit submission of a Phase II application. Phase II work will focus on obtaining the preclinical data necessary for submission of an IND. Initial CMC work, pharmacokinetics and toxicology, as well as expanded animal studies will be performed.